1. Field of the Invention
The present invention relates to a back light unit of a display panel, and more particularly, a back light unit having a high heat transfer rate.
2. Description of the Prior Art
A back light unit, which is a key element in the fabrication of liquid crystal displays, is widely used in digital cameras, PDAs, vehicle satellite navigation systems, computer monitors, flat panel TVs, and so on. Typically, a back light unit, which is generally installed underneath a display panel, comprises a light source (or multiple light sources) and a light diffusion plates for providing users with diffused and uniform light beams. Light beams penetrate the overlying display panel and form various images controlled by pixel electrodes densely arranged on the display panel. Back light units are typically divided into two major categories: direct-type, in which the light source is generated form underneath the display panel directly, and edge light type, in which the light source generator is located adjacent to the edge of the display panel. The direct-type backlight unit can provide higher intensity of light and is thus more suited for large size display panels such as computer monitors and TV panels than the edge light type.
Please refer to FIG. 1 of a cross-sectional view of a conventional back light unit 10. The back light unit 10 is installed underneath a display panel 12 and comprises a light source generator 14, a diffusing plate 16 interposed between the light source generator 14 and the display panel 12, and a reflecting sheet 18 disposed under the light source generator 14 and fixed on a housing 20. The light source generator 14 is used to provide a light source to the display panel 12. The reflection plate 18 is used to reflect light generated by the light source generator 14 upward to the overlying diffusing plate 16, thereby increasing light use efficiency of the back light unit 10 and obtaining a better brightness output. The diffusing plate 16 is used to diffuse light (or reflected light) by means of shielding, scattering, or refraction so as to provide a uniform light to the display panel 12. The housing 20, which is disposed beneath the reflecting sheet 18 and surrounding the reflecting sheet 18, is used to fix the diffusing plate 16, the reflecting sheet 18, and the light source generator 14. In addition, a diffusing sheet 22 and an optic focusing film 24 are typically provided above the diffusing plate 16 for enhancing the back light unit 10 so as to output light beams with uniform luminous intensity to the display panel 12. The number and the position of the diffusing sheet 22 and the optical focusing film 24 can be varied according to the requirements of the products.
The light source generator 14 in the back light unit 10 is typically composed of a plurality of light tubes. To meet the requirements of high brightness and low weight, the aforementioned light source generator 14 is often installed in a closed chamber which is very narrow and small. Thus, the heat generated during operation accumulates rapidly, leading to a high temperature near the light tubes after operating for a period of time. The high temperature interferes with the normal operation of the display panel 12 and deteriorates the display performance. For example, distortion easily occurs on the screen. This leads to a decrease in the lifetime of devices nearby.
Consequently, there is a strong need to provide a back light unit with a high heat transfer rate to improve the display performance and lengthen the lifetime of devices in the back light unit.